EP0391791B1 - Multi-phase synchronous machine with permanent magnets - Google Patents

Description

The present invention relates to a synchronous electrodynamic machine with permanent magnets comprising a rotor of the flux concentration type comprising a shaft or a hub made of non-magnetic material on which rest permanent parallelepipedal radial magnets between which the pole pieces made of sheet metal are placed. ferro-silicon magnetic and a stator comprising a carcass made of ferro-silicon magnetic sheet in which are formed a plurality of semi-closed notches delimited by a stator yoke which receive induced windings, and which defines with the rotor an air gap.

In the machines described above, to obtain a high mass torque, we use rotors fitted with so-called high energy magnets, of rare earth type (Samarium Cobalt and more recently Neodymium-Iron), sometimes calling, in the best of cases , to a magnetic rotor structure, known to those skilled in the art, the flux concentration structure. This approach is suitable for machines with relatively low torques and rotating at high speeds, therefore driving loads via reducers.

However, when it is desired to carry out direct drive of loads without reducers, at a given power, the torque required at the motor is much higher than in the motor-reducer solution, we are therefore led to machines of dimensions in which the use of rare earth magnets of high specific price leads to a very high cost of the machine dissuading the user from using a Direct Drive solution, while technically, for reasons of play, stiffness, increase in servo bandwidth, and simplicity of mechanical implementation, Direct Drive is desirable.

The subject of the invention is the production of synchronous machines with permanent magnets with high mass and volume torque, rotating at slow speed which allows direct drive.

• l'utilisation de rotors de diamètre élevé (supérieur à 100 mm) compatibles pour l'utilisateur avec les couples requis (de 25 Nm à plusieurs centaines de Nm).
• l'utilisation de rotors à concentration de flux à grand nombre de pôles ; les pertes magnétiques restant cependant faibles du fait des faibles vitesses de rotation nécessitées par l'Entraînement Direct (quelques tours/s, généralement moins de 3 trs/s).

The object of the invention is to obtain high flux concentration ratios in order to have, with ferrite type magnets, a flux emanating from the rotor close to that which would be obtained with high energy rare earth magnets. On the other hand, these large flux concentration ratios make it possible to obtain a stator induction close to the saturation induction. This is made possible by:

• the use of large diameter rotors (greater than 100 mm) compatible for the user with the required torques (from 25 Nm to several hundred Nm).
• the use of flux concentration rotors with a large number of poles; however, the magnetic losses remain low due to the low rotational speeds required by the Direct Drive (a few turns / s, generally less than 3 trs / s).

The ferrite magnets are interesting from the point of view of the cost because their specific price is of the order of fiftieth that of the magnets Samarium - Cobalt currently, and of the twenty-fifth of that which will reach after stabilization the new rare earth magnets high-energy iron neodymiums, which exhibit large coefficients of field loss with increasing temperature. Consequently, the solution according to the invention is competitive compared to traditional solutions with geared motors.

Note that the use of magnets of high energy type would bring a significant additional cost with the same structure, but would not bring a significant gain in mass torque because the coefficient of flux concentration would be lower than that practiced for ferrites, sheets magnets used for the stator magnetic circuit, saturating magnetically around a 2 Tesla induction already achieved with the machine according to the invention.

To obtain these results, the machine according to the invention is characterized in that the magnets are of the ferrite type and that the ratio r1 of the height of the section of a magnet traversed by the induction flux divided by the diameter of air gap bore is between 0.19 and 0.27.

According to another characteristic of the invention, the ratio r2 of the height of the section of a magnet crossed by the false induction divided by the length of a peripheral polar half-arc of the rotor separating the facing faces - screw of two consecutive magnets or flux concentration ratio is between 3.1 and 3.9. According to another characteristic, the ratio r3 between the product of the number of stator teeth multiplied by the thickness of a stator tooth separating two consecutive notches, divided by 4.P times the length of a peripheral polar half-arc of the rotor separating the facing faces of two consecutive magnets, P being the number of pairs of poles of the machine is between 0.75 and 0.95.

According to another characteristic, the ratio r4 of 4.P times the radial thickness of the stator yoke divided by the product of the number of stator teeth separating the stator notches by the thickness of a stator tooth separating two consecutive notches 0.60 and 0.75.

We have thus just defined a series of dimensioning ratios r1 to r4 which make it possible, from the initial choice of a bore diameter, to determine the set of dimensions of the machine making it possible to obtain a maximum mass torque with use. ferro-silicon magnetic sheets and ferrite magnets. This series of optimal ratios leads to a rotor structure with quasi-contiguous magnets at their lower end.

• la figure 1 est une vue en coupe axiale d'une machine électrodynamique synchrone.
• la figure 2 est une vue schématique en coupe transversale du rotor et de la carcasse d'une machine électrodynamique réalisée conformément aux enseignements de la présente invention.

The invention will now be described with reference to the accompanying drawings in which:

• Figure 1 is an axial sectional view of a synchronous electrodynamic machine.
• Figure 2 is a schematic cross-sectional view of the rotor and the carcass of an electrodynamic machine produced in accordance with the teachings of the present invention.

FIG. 1 shows an axial section of a synchronous motor.

The motor essentially comprises a casing (1) in which a stator (2) is mounted, the internal peripheral wall (3) of which co-operates with the external peripheral wall (4) of a rotor (5) mounted in the casing (1) for define an air gap (6) between them. The rotor (5) is mounted rotating in the casing (1) by means of two bearings (7) and (8) each comprising a bearing.

The stator (2) shown in Figures 1 and 2 comprises a main stator winding (9) disposed in the semi-closed notches (10) delimited by a stator yoke (11).

The rotor (5) also includes magnets (12) mounted in radial notches (13).

In the context of the present invention, the magnetic sheets in which the pole pieces (14) and the yoke (11) are made are ordinary sheets made of ferro-silicon alloy.

Each of the rotor magnets has a generally rectangular parallelepiped shape and is supported on the non-magnetic shaft or hub (15).

The magnets used are ferrite magnets. In the embodiment presented, the magnets each consist of a plurality of elementary parallelepiped magnets (12) assembled together and this for manufacturing facilities.

dans laquelle

• h est la hauteur radiale de la section S d'un aimant (12) traversée par le flux d'induction, et
• d est le "diamètre d'alésage" ou diamètre moyen de l'entrefer (6) de la machine électrodynamique, est compris entre 0,19 et 0,27 aux détails de réalisation près.

Each magnet is magnetized tangentially, that is to say that the lines of flux exiting through a lateral section S of a magnet are substantially perpendicular to the radii of the rotor. In accordance with the invention and in order to obtain the maximum magnetic saturation, the electrodynamic machine is dimensioned so that the ratio r1 defined by the formula $$\text{r1 =}\frac{\text{h}}{\text{d}}$$

in which

• h is the radial height of the section S of a magnet (12) traversed by the induction flux, and
• d is the "bore diameter" or average diameter of the air gap (6) of the electrodynamic machine, is between 0.19 and 0.27 to the details of construction.

dans laquelle
- a est la longueur d'un demi-arc polaire périphérique externe du rotor (5) séparant les faces S en vis-à-vis de deux aimants consécutifs (12), est compris entre 3, 1 et 3,9.According to another characteristic of the invention, the ratio r2 defined by the formula $$\text{R2 =}\frac{\text{b}}{\text{at}}$$

in which
- A is the length of an external peripheral polar half-arc of the rotor (5) separating the faces S facing two consecutive magnets (12), is between 3, 1 and 3.9.

dans laquelle

• n est le nombre de dents statoriques (16) séparant les encoches statoriques (10).
• e est l'épaisseur d'une dent statorique (16) séparant deux encoches statoriques consécutives (10).
• P est le nombre de paires de pôles magnétiques, est compris entre 0,75 et 0,95.

According to another characteristic of the invention, the ratio r3 defined by the formula $$\text{r3 =}\frac{\text{born}}{\text{4.Pa}}$$

in which

• n is the number of stator teeth (16) separating the stator notches (10).
• e is the thickness of a stator tooth (16) separating two consecutive stator notches (10).
• P is the number of pairs of magnetic poles, is between 0.75 and 0.95.

According to a preferred embodiment, the number of pairs of poles is equal to 6, the number of stator teeth (16) is equal to 72.

dans laquelle
c est l'épaisseur radiale de la culasse statorique (11) délimitant les encoches statoriques (10), est compris entre 0,60 et 0,75.According to another characteristic of the invention, the ratio r4 defined by the formula $$\text{r4 =}\frac{\text{4.Pc}}{\text{born}}$$

in which
c is the radial thickness of the stator yoke (11) delimiting the stator notches (10), is between 0.60 and 0.75.

Claims (5)

1. A synchronous electrodynamic machine with permanent magnets comprising a rotor (5) of the flux concentration type comprising a shaft or a hub (15) constructed in non-magnetic material on which rest parallelepipedic radial permanent magnets (12) between which are disposed the polar pieces(14) constructed in ferrosilicon magnetic sheet and a stator (2) comprising a frame constructed in ferrosilicon magnetic sheet in which are formed a plurality of semi-closed slots (10) delimited by a stator yoke (11) which receive armature windings (9) and which defines with the rotor (5) an air gap (6) characterised in that the magnets (12) are of ferrite type and in that the ratio r1 of the height (h) of the section (S) of a magnet (12) through which passes the induction flux divided by the bore diameter (d) of the air gap is between 0.19 and 0.27.
2. The machine according to Claim 1 characterised in that the ratio r2 of the height (h) of the section (S) of a magnet through which passes the induction flux divided by the length (a) of a peripheral polar half-arc of the rotor (5) separating the opposite faces of two consecutive magnets (12) or flux concentration ratio is between 3.1 and 3.9.
3. The machine according to any one of the preceding claims, characterised in that the ratio r3 between the product of the number (n) of stator teeth (16) multiplied by the thickness (e) of one stator tooth (16) separating two consecutive slots (10) divided by 4.P times the length (a) of a peripheral polar half-arc of the rotor (5) separating the opposite faces of two consecutive magnets (12), P being the number of pairs of magnetic poles, is between 0.75 and 0.95.
4. The machine according to any one of the preceding claims characterised in that the ratio r4 of 4.P times the radial thickness (c) of the stator yoke (11) divided by the product of the number (n) of stator teeth (16) separating the stator slots (10) by the thickness (e) of one stator tooth (16) separating two consecutive slots (10) is between 0.60 and 0.75.
5. The machine according to any of the preceding claims characterised in that the number P of pairs of magnetic poles is equal to 6.

Images